1. Field of the Invention
This invention relates to fire alarm systems, and is more particularly concerned with a process for generating and transmitting different analog values to a central control from a plurality of fire alarm circuits which are connected in a chain fashion in an alarm loop.
2. Description of the Prior Art
It is well known in the art to transmit different analog measured values to a central control from a plurality of fire alarm circuits which are arranged in the form of a chain in an alarm loop, hereinafter called the alarm line, and which prior to interrogation are disconnected from the alarm line by a voltage change and are then supplied with current by individual respective capacitors which can be charged during connection of the full line voltage. The individual alarms can be subsequently reconnected to the alarm line in a given sequence by a new voltage change (at a reduced line voltage). Each preceding line circuit connects the following alarm circuit to the line voltage with a time delay representing the measured value of the fire characteristic and in a central analysis device the relevant alarm circuit address can be determined from the number of preceding increases in line current and the associated measured value can be derived from the length of the switch delay of the corresponding alarm circuit.
In the event of a breakdown in the commercial power supply, firm alarm systems are to be supplied by a second, independent energy source for a minimum length of time. Generally speaking, batteries serve as such a second, independent source. The requisite capacity of this emergency current supply is determined, on the one hand, by the current drain of the alarm central control and, on the other hand, by the number of alarm circuits connected to the central control. As mentioned above with respect to the prior art, through chain synchronization, the analog measured values and the alarm circuit addresses can be transmitted in a simple fashion to the central control for appropriate analysis. Capacitors in the alarm circuits are charged following the interrogation with normal line voltage and, in this manner, in the periods of time in which no voltage is connected to the line, the capacitors are able to feed the alarm circuits and thus bridge these breakdown times.